Although anti-tachycardia pacing is a valuable treatment technique, the pacemakers presently available do not effectively discriminate among the various arrhythmias. The project proposed herein will use data gathered from electrophysiologic studies and pacemaker procedures to aid in design of a sensing system for multifunction pacemakers. The data will be recorded on a Hewlett Packard 396A PM magnetic tape recorder and analyzed in the time domain by use of filters and a Biomation Waveform recorder (1015) and in the frequency domain (Fourier and Walsh transforms) by use of DEC PDP 8/e and Minc 11 computers. A software prototype has been programmed on the PDP 8/e using digital filters and timing algorithms. Single site algorithms will be compared with multi-site methods for discriminating arrhythmias, and the prototypes will be tested on recorded data. The system which appears most satisfactory, will be constructed as a hardware circuit and further tested on recorded clinical data. A future project may involve testing during human clinical studies. No testing on humans is planned for this project. The feasibility of miniaturization of the prototype to a size that could be included in an implantable pacemaker will be investigated. An unknown but probably substantial portion of the estimated one million persons seen for tachycardias nationwide annually could benefit from anti-tachycardia pacing. Very few of these persons are now paced due to the limited effectiveness of the primitive automatic units and the limited applicability of the manual units presently available. This project represents a joint venture of cardiac surgeons, cardiologists, technicans, bioengineers and nurses, all of whom are specialists in pacemakers and cardiac electrophysiology. The data from over 300 procedures performed annually combined with the laboratory facilities available for analysis of the data represents a unique ability to develop the "universal" sensing system for cardiac pacemakers.